1. Field of the Invention
The present invention relates to hand held portable power tools such as string trimmers and more specifically to a coupling structure for selectively attaching a lower boom section with any of a variety of work tools such as a trimmer, edger, blower, cultivator or brush cutter to an upper boom section having a power source such as a gasoline engine or electric motor.
2. Description of the Related Art
Those who provide lawn care services and others who maintain lawn, shrubs and trees frequently utilize hand held power tools such as string trimmers, edgers, blowers, brush cutters and cultivators. These hand held power tools typically include a gas engine or electric motor coupled to an elongated boom with the work tool at its opposite end. A flexible or solid shaft is driven by the engine or motor to rotatably power the work tool.
In the past, it has been necessary to purchase and maintain separate hand held power tools capable of performing each such type task. Recent developments in split boom tools have reduced the need to have separate power tools for each task by making the lower portion of the hand held tool detachable and providing multiple attachments with varied work tools that can be interchangeably used with a common upper boom and engine or motor. An example of the structures utilized which provide this capability can be found in U.S. Pat. No. 4,733,471.
Present split boom power tools typically provide for upper and lower boom sections that are separable in the mid-section of the boom and for a flex drive shaft that can be easily disengaged and/or engaged when the boom sections are uncoupled or coupled. Their coupling structures utilize clamping sleeves into which the adjacent ends of the boom sections are inserted. A plurality of openings circumferentially spaced around the upper boom tube and clamping sleeve allow a locking pin to be variably positioned to orient the work tool, that is, the trimmer head, edger or blower at its proper angle with the upper boom for work. The clamping sleeve which secures the adjacent ends of the boom sections together is squeezed or tightened by the use of two or more screw type fasteners.
Present split boom coupling structures fail to provide for positive and easy positioning of the clamping structure and upper and lower boom members at the joint, telescopically joining of the upper and lower boom sections together or reinforcement of the coupling joint.
The present coupling structure overcomes these problems and provides for quickly and positively positioning the clamping structure through use of a locating tab on the clamping member that is receivable in a locating opening in the end portion of the upper boom section. As the tab positions the clamping structure with the upper boom member, it also aligns a plurality of tool orienting openings in the clamping structure with similar openings provided in the upper boom member. Further, an enlarged tubular cross section on the lower end of the upper boom section allows a comparatively smaller tubular end of the lower boom section to be quickly and easily positioned, inserted and joined together. Through telescopically joining and overlapping the adjacent ends of the upper and lower boom sections, the joint between them is thereby strengthened.
With the improved coupling structure, any of a variety of lower boom tools can be quickly, easily and positively attached with and aligned to the proper angular position with the upper boom section.